1. Field of the Invention
The present disclosure relates to an image forming system including inkjet heads configured to eject ink to a sheet to form an image.
2. Description of the Related Art
A serial recording system or a line head recording system is applied to most of image forming apparatuses with printing functions for forming images using ink (printers, multi-functional peripherals, etc.). The serial recording system includes a recording head configured to scan a sheet. The line head recording system includes a fixed head unit.
The head unit used for the image forming apparatus with the line head recording system ejects the ink onto a conveyed sheet to effect a recording operation. The head unit includes a plurality of ejection ports arranged in accordance with the width dimension of the sheet.
Many types of image forming apparatuses are configured to effect printing operation on various sizes of sheets. The length of the fixed recording head mentioned above is set in accordance with the width of the largest sheet. In many cases, the head unit includes a plurality of connected heads in order to ensure a printing area large enough for the largest sheet. The head unit with the plurality of heads is produced relatively easily.
The alignment of the ejection ports in the head unit in a direction substantially perpendicular to the sheet conveying direction significantly affects qualities of an image to be formed. The heads therefore have to be connected carefully. An excessively wide space between the ejection ports at a connection portion of the heads causes a defective area, where the ink does not adhere in an image formed on the sheet. The defective area where the ink does not adhere to the image looks like a stripe extending along the conveying direction of the sheet. An excessively narrow space between the ejection ports at the connection portion of the heads causes a partial or overall overlap of dots of the ink ejected from the ejection ports at the connection portion. The overlapped dots results in a deeper printing area on the formed image. As a result, the highly deeper printing area looks like an outstanding stripe on the sheet. Therefore, the distance between the ejection ports at the connection portion of the heads has to be determined very carefully.
A specific head unit includes a pair of heads partially overlapped so as to align a pair of ejection ports in the sheet conveying direction in the connected part between the heads. The ejection of the ink from the pair of ejection ports is switched selectively.
The heads including the pair of ejection ports mentioned above are positioned on a supporting board. The heads has to be mounted onto the supporting board very accurately in order to prevent the formation of the stripe on the sheet by selectively ejecting the ink from the pair of ejection ports.
In order to check if the heads are mounted onto an appropriate position or not, a user forms an image on the sheet by ejecting the ink from the heads mounted onto the supporting board. The user then measures a relative space between dots of the ink forming the image through microscopic observation. When the heads are mounted onto inappropriate positions, the user displaces the heads on the supporting board and checks the space again. Therefore, the user is required to perform a complicated adjustment work for positioning the heads according to the conventional manner.